High-frequency alternator



Jan. 21, 1930. J. BETHENOD ET AL HIGH FREQUENCY ALTERNATOR 2Sheets-Sheet 1 Filed Aug. 29. 1921 QnswMw W JBETHEHQ E EGIRARDEHU Jan.21, 1930. J. BETHENOD ET AL HIGH FREQUENCY ALTERNATOR Filed Aug. 29.1921 2 Sheets-Sheet 2 39 gsiq 7 [.GIRARDEFIU I wwaumm Patented Jan. 21,1930 UNITED STATES PATENT OFFICE JOSEPH BETHENOD AND EMILE GIRARDEAU, FPARIS, FRANCE HIGH-FREQUENCY ALTERNATOR Application filed August 29,1921. Serial No. 496,552, and in France August We have filedapplications as follows: France, filed Aug. 10th, 1915, granted No.492,414; France, filed Jan. 30th, 1919, granted N 0. 21,730; Germany,filed Mar. 3rd, 1921;

5 Great Britain, filed July 26th, 1916, granted No. 101,148; GreatBritain, filed July 26th, 1916, granted No. 103,657; Great Britain,filed July 26th,-1916, granted No. 103,658; Belgium, filed May 15th,1920, granted No.

287,154; Brazil, filed June 14th, 1920; China (custom house, Shanghai),filed Aug. 16th, 1920, No. of registration 21,041; Belgian Congoland,filed May 17th, 1920, granted No. 590; Denmark, filed Jan. th, 1920;Spain,

filed Dec. 20th, 1919, granted No. 71,809; Netherlands, filed May 6th,1920; Italy, filed Apr. 15th, 1920, granted No. 184,033; Morocco, filedApril 19th, 1920, granted No. 144; Norway, filed Jan. 17th, 1920,granted No.

ac 37,309; Poland, filed July 6th 1920; Portugal, filed May 11th, 1920,granted No. 11,434; Rumania, filed July 3rd, 1920, granted No. 5,310;Sweden, filed Dec. 31st, 1919, granted No. 54,909; Switzerland, filedDec. 8th, 1919,

2;; granted No. 94,335; Czechoslovakia, filed May 4th, 1920; TunisieuProtectorate, filed Apr. th,'1920, granted No. 1,704.

This invention relates to apparatus for use in wireless telegraphy andwireless telephzo ony and particularly to a high frequency alternatorfor use in connection therewith.

An object of our invention is to provide a high frequency alternator ofsimple construction, reliable operation and substantially lower speedthan those now in use for the same frequency.

A further object of our invention is to provide a high frequencyalternator in which a harmonic of the fundamental frequency of the waveof the machine is utilized to raise the frequency of the output.

A further object of our invention is to provide an alternator in whichthe amplitude of a harmonic of the fundamental frequency is 43 increasedat the expense of the amplitude of the fundamental, thereby raising thefrequency of the output of the alternator.

A further object of our invention is to provide a high frequencyalternator in which certain harmonics of the wave form are eecentuatedand the fundamental is suppressed. A further object of our invention isto provide a hlgh frequency alternator in which a certain harmonic ofthe wave form is accentuated and-the fundamental is suppressed byud1c1ously choosing the width and pitch of the teeth of the rotor andstator.

Our invention is particularly adapted to alternators of the variableimpedance type but is not limited to such machines, being adapted alsoto alternators of the homopolar type. It will be described hereinafteras applied to both types.

For a detailed description reference is made to the accompanying drawingin which Fig. 1 1s a system employing a high freguency alternatorconforming to our invenion, 4

Fig. 2 is a diagrammatic showing of the rotor and stator teeth of analternator of the yariable lmpedance type conforming to the inventlon,

Fig. 3 is a connection diagram illustrating a plurallty of alternatorsconnected in cascadev to feed'the same antenna,

Fig. 4 is a detailed view illustrating a method of holding the statorwindings in their slots,

Fig. 5 is a diagrammatic showing similar to Figure 2, but illustratinour invention ztis applied to an alternator of the homopolar Figs. 6 and7 are sectional views, at right angles to each other, illustrating apluralit of alternators mounted on a common sha t according to theinvention and Fig. 8 is a detail view showing the rotor and stator teethof a homopolar alternator conforming to the invention and comprising acomposite rotor.

The attempts hitherto made to produce directly the hi h frequencyoscillations that are necessary or the transmission of wirelesstelegraphic and telephonic signals consisting in the use of machinescomprising 96 rotors or moving members have given rise to theestablishment of hi h frequency generators, the construction 0 whichinvolves very heavy expense and results in serious technicaldifliculties.

Among the technical difliculties existing in previous installations thefollowing may be enumerated.

1. Those met with in the use of cascade alternators comprising a woundrotor Since the peripheral velocity is always considerable, even withthe cascade arrangement, and since moreover the useful periphcry of therotors should consist of segments of extra thin sheet iron (havingregard to the impossibility of manufacturing with a thickness less thanof a millimetre, sheet iron lates of dimensions sufliciently large toena lo the rings necessar for a high power machine to be cut out terefrom in one piece), these alternators are very costly to constructand always present very great mechanical risks. In fact the incongruouscollection of segments of extra thin sheet iron held by dovetailing, ofcables forming the winding of the rotor, and of insulating materialpossesses none of the qualities required for resisting with sufficientsafety the effects of centrifugal force.

2. Those met with in. the use of static freguency transformers It hasbeen suggested that by the use of frequency changing apparatus, such asstatic frequency transformers, a relatively lower frequency generatormay be utilized for feedin the same which generator may be better adapted to stand the strains incident to use. However, such an arrangementis not fully satisfactory because of the indifferent output of suchapparatus and because of the technical difliculties, both practical andtheoretical, that their construction involves as well as othercomplications they introduce into the installation.

It is to be observed morever, that the solutions recalled under headingsNos. 1 and 2, which in spite of their defects are the only ones thatappear up to the present moment to have been carried into ractice on alarge scale, necessitate the use of exceedingly powerful cooling methodsor devices which can onl be effected with difliculty.

gar invention will first be described in connection with a highfrequency machine of the variable impedance t pe, without windings onthe rotor, the fun amental frequency of which is of the order of 5,000to 15,000 alternations per second. The frequency which we obtain fromthe machine however is much higher than this fundamental frequenc as wemake use of one of the harmonics o the wave of the machine therebymultiplying the fundamental frequency. by 3, 5, 7 or some other factordepending on the harmonic which is utilized.

The installation hereinafter described and forming the subject of thepresent invention employs an alternator of a new or improved type, therotor of which has -no winding, that is to sa which is free of suchcriticism as referre to in relation to cascade machines.

Furthermore the multiplication of frequency operates in the machineitself, that is to say, under conditions of efficiency and simplicityincomparably superior to those obtained by separate static transformers.

Variable-impedance machines are already known that do not comprise anwindings on the rotor, see J. Bethenod, ulletin de la SocieteInternationale des Electriciens, Third Series, Volume IV, No. 36, 1914.

In such machines as therein stated, the rotor consists of a toothed discof sheet iron, having as many slots as possible; round this rotoris'placed a stator having the same number of teeth as the rotor andprovided with a single winding so wound on the teeth that they,considered successively, are of alternate polarity.

Under these conditions, if the current from a continuous-current sourceis sent into this winding, there is obviously produced in the winding analternating current that is superposed on the continuous excitingcurrent, and which is capable of feeding for example a radio-telegraphicantenna through a transformer or if desired an inductance or a capacityor both may obviously be used for the antenna connection.

The machine just described was proposed by Joseph Bethenod in 1907 forradiotelegraphy. He pointed out at that time that the fundamentalfrequency of such a machine is given by the formula: (1)' f=mn where nequals the number of revolutions per second and m the number of teeth ofthe stator (in this case of the rotor also).

If m be regarded strictly as the number of stator teeth then m teethonly form in reality m poles, and the machine in question furnishes,under equal conditions, double the fundamental frequency obtained withan alternator of the type ordinarily employed for low frequency, i. e.an alternator wherein the number of pole windings on the rotor is equalto the number of stator poles, whereby the frequency equals the numberof revolutions multiplied by the number of pole pairs, or with anundulating flux machine having two armature cores arranged on the statorand separated by an inductor, the cores and inductor being magnetized bya field coil, also fixed, concentric with the axis of rotation, eacharmature or stator core having double the number of inductor teeth. Seethe Alexanderson machine shown on page 402 of the Transactions of theAmerican Institute of Electrical Engineers. Vol. XXVIII (1909), andreferred to by Bethenod in the above cited bulletin.

The above described Bethenod machine possesses two defects aboverelative to the high frequency obtained, the latter cannot be raisedsufficiently high to correspond to a wave length of 10,000 metres unlessexcessive peripheral velocities are adopted; a supplementary multilication of frequency is therefore impose in the majority of cases.

(2) The rotor should obviously be of thin laminated sheet iron, althoughit is not provided with windings, which presents advantages(particularly for a rotor constructed in several segments) over theGoldschmiclt machines and cascade machines.

According to the present invention, the first defect has been remediedin the following manner.

Referring now to Figs. 1 and 2 of the drawing, which illustrate theapplication of our invention to machines of the variable impedance type,S represents the stator with teeth A and slots B and R represents therotor with teeth C and slots D. On the stator S is the winding Z whichis wound op-. positely on each successive tooth thereby causing thestator teeth to become alternately north and south poles when thewinding is energized with direct current. It will be noted that,whereas, in the older type of machine, described above, the teeth andintervening slots were of equal peripheral width on both the stator androtor, in our machine the slots on both the stator and rotor areconsiderably wider than the teeth. In the machine shown in Figs. 1 and 2the width of the rotor teeth is equal to the Width of the stator teethand the width of the rotor grooves is equal to the width of the statorgrooves.

The older type of machine does not give a sinusoidal E. M. F. curve offrequency 7 (Formula 1) for that it would be necessary that the fluxvariation produced by the displacement of the rotor should be simple.

harmonic, which is not the case in practice.

An E. M. F. is therefore obtained, the expression for which, developedaccording to the Fourier series, contains harmonic terms in 2', 3, etc.

The mathematical analysis of this series shows that the relativeamplitude of any term depends on the ratio between the width- 12 of theteeth (Figure 2) of the stator S or of the rotor R, to the common pitchp of the teeth (this pitch being equal to d plus e the width of slot),and that the harmonic of rank (1 will reach its maximum amplitude whenOf course (i will in practice be the actual ma etic breadth, i. e. thecircumferential wi th, at the air ap, of the extremity of the tooth,plus the efiective width of the fringe formed by the flux at its exitfrom the tooth.

This harmonic, which is in this way rendered very marked, is utilized,accordln to the present invention, for the direct fee ing of theantenna. Most often g=2 or g=3 will be chosen; doubling or trebling ofthe fundamental frequency will then be obtained, and this choice leadsin practice to a machine without excessive magnetic leakage into theslots or notches, the teeth however being mechanically of ampledimensions when the wave-length of the antenna is ofthe order of 10,000metres, (as employed in large modern stations).

In order to eliminate from the external circuit every current offundamental frequency, as well as the unused harmonics, it is possible(a) Either to arrange in series in the electric circuits actual dams forthe currents of a particular frequenc to this end systems will be usedthat are ormed for example by putting an inductance and a capacity inparallel, the whole so constituted being damped as little as possible,and being syntonised with the frequency of the currents to beeliminated.

(6) Or to create short circuits for the stray electro-motive forces;this may be attained by means of resonators formed by putting a capacityand an inductance in series, the whole so constituted being again dampedas little as possible, and being syntonised with the frequency of the E.M. F.s to be eliminated, and shunted to the armature winding of thegenerator.

It will be noted that the fundamental frequency of the machine is afunction of the number of teeth on the rotor and the speed of themachine in accordance with the equation =mn (1), this relation, ofcourse applying to our improved machine as well as the older type.However by dimensioning the relative widths of the teeth and slots inaccordance with the relation (1 in which 9 represents the order of theharmonic which is to be utilized, the amplitude of this harmonic will bemuch increawd and the machine can therefore be used as a source ofenergy of a frequency several times its fundamental frequency.

In Fig. 1 the alternator is shown connected to an antenna to serve as ahigh frequency source of energy. The winding E is connected to a sourceof direct current represented by a battery P, an inductance B beingconnected in the battery circuit to prevent the high frequency currentfrom the alternator from reaching the battery. The winding E is thusenergized and causes the stator teeth to become magnetized to formalternate north and south poles. It is obvious that as the rotor teethsweep past the stator teeth there will be changes in the impedance ofthe winding and these changes cause an alternating current to be inducedin the winding E, this current being superimposed on the energizingdirect current. The frequency of this current as stated above is equalto the number of rotor teeth multiplied by the speed of rotation of therotor in revolutions per second. This is the fundamental frequency ofthe machine. Owing to the spacing and width of the stator and rotorteeth the amplitude of the fundamental wave is very small as compared tothe amplitude of one of its harmonics. The particular harmonic which isthus accentuated is determined by the spacing and width of the teeth asdetermined by the formula d= given above.

The alternator in Fig. 1 is shown connected circuit to eliminate thecurrents of the fundamental frequency of the alternator but to freelypermit the passage of currents of the chosen harmonic. By manipulatingthe key M, waves of several times the fundamental frequency of thealternator can be sent from the antenna.

Finally, by connecting in series 9 machines mechanically coupled in sucha Way that they possess a regular electrical phase-displacement of everycurrent is eliminated the frequency of which is not a multiple of q. Anarrangement of this nature is shown diagrammatically in Figures 6 and 7in which 21 is a common shaft supporting three sets of rotor teethnamely, 19, 19 and 19" which are so supported on the shaft as to beelectrically f) displaced from each other in phase by g Each set ofrotor teeth co-operates with a separate stator 18, 18', and 18",respectively, which are identical with each other and in the presentcase are shown as mounted on a common member 15 in alignment axially ofthe shaft 21. The several stators are energized by suitable windings 17located and conveniently supported in slots between the stator teeth.This structure comprises substantially three separate alternatorsmechanically coupled so that there is a regular phase displaced betweentheir output currents.

Figure 3 shows a circuit arrangement for such a connection for q=3, thewindings E, E, E" representing respectively the windings of threedifferent machines having a phase-displacement of agthe capacity C butthese details may be varied without departing from the nature of thepresent invention.

Instead of providing g separate machines, the same elimination may bearrived at by using on the rotor q times as many teeth as on the stator,the breadth common to the stator and rotor teeth always being determinedby formula (2) and 1) being then the pitch of the stator teeth only.This solution is in general suitable only for low frequencies.

The second mechanical defect referred to in the introduction, iscompletely eliminated in accordance with the present invention. Thesection of Fig. 4 shows the details of a machine of this new type, andthe great security obtained by means of this machine will be obviousfrom an examination of this figure. Therotor R (shown open the same wayas the stator S) comprises segments of sheet-iron cut out like Y, andseparated from each other by means of joints J. J. These segments areheld in place on the massive ferrule F (or on a drum forming a unitarystructure with the shaft of the machine) by means of tenons H providedin the grooves on the same side. An important feature of the inventionto be noted is that, on account of the relatively small width of theteeth with respect to their pitch (the drawing corresponds to q=3,whereby d= as many tenons H are provided as there are teeth, and thesheet-iron bridges connecting the teeth are only of such a slight heightas is necessary for the passage of the flux. Each tooth is thusindividually anchored to the shaft without the necessity of subjectingthe bridges to appreciable strain. In order to avoid the multiplicationof the magnetic joints J, the teeth provided with their tenons are notseparately stamped out. The shape of these tenons constitutes also acharacteristic feature of the invention. Its advantages over the usualdove-tailing consists in that it has progressive curves of great radius,i. 0. does not form any weak spot in the profile herein adopted. Aswell-known, the small radius curvatures of the dove-tails cause quiteoften local strains that may bring about the splitting of the wholeassembly. The conductors Z may be maintained in their slots by anyconvenient means, one very good method being illustrated in Fig. 4. Inorder to locate the conductors Z as near as possible to' the air-gap,and preferably they should be located in this manner for obtaining themaximum variation of useful flux, the following arrangement may beadopted; at certain distances in the sheet iron structure of the rotor,cut out in accordance with Fig. 4, non-magnetic sheets are inserted andare provided with half-closed notches. These nonmagnetic sheets willmaintain the stator windings due to the shape of the notches provided inthese sheets, and the teeth of the sheets of non-magnetic material, theends of which are shown pointed, would be of the minimum length that isnecessary for reventing contact between the stator win in and the rotor.It should be noted that, the circular section of the conductors of thestator shown in Fig. 4 is not indispensable, and a section of anysuitable shape may be adopted in each individual case.

In the preceding description provision is made for the application ofthe devices previously described in connection with variable impedancemachines. to homopolar machines having energizing windings concentricwith the shaft.

Such a machine is illustrated diagrammatically in Fig. 5. The teeth C"in this figure are all magnetized to the same polarity by any convenientmeans (not shown). In a homopolar machine it is of course necessary fora rotor tooth to sweep past two complete stator teeth to induce acomplete alternation in the stator winding and therefore there must betwice as many stator teeth for a given number of rotor teeth in thehomopolar type as in the variable impedance type. Thls is shown in Fig.5 in which there are shown two stator teeth for each rotor tooth. Bydimensioning and spacing the rotor teeth in the same wa as in thevariable impedance type, that is in accordance with the equation d= g g:any desired harmonic represented by r] can be accentuated in the sameway as in the variable impedance type. The frequency of the output ofthe homopolar type can therefore be made a multiple of its fundamentalfrequency.

As in the case of the variable impedance type 9 machines may beconnected in series. The machines possess an electricalphase-displacement of 27-1- for the purpose of eliminating all currents,the frequency of which is not a multiple of q. The dimensions of themachines are chosen in a manner whereby they possess a harmonic of themultiple 9 the formula in which g is the number of number of rotor teethowing to the'fact that each pair of stator serves for a plurality ofsets of rotor teeth. For one of the stator teeth is only of the numberof g rotor teeth, in which n is an integer depending on the harmonic tobe accentuated.

This relationship can best be explained by a concrete example and inFigure 8 a combined machine designed to accentuate the third harmonic isshown. In this case n=1. By referring to Fig. 8 it will be noted thatthere are three rotor teeth, representing three machines for each pairof stator teeth. Preferably, the profile of the teeth and the notchesdescribed previously for variable inductance machines, should bepreserved, and the periphery of the rotor should be composed of thinsheet-iron, fitted into the massive core by means of tenons having roundcontours, as already described.

The width of the rotor teeth at the air gap should be preferably equalto the width of the stator teeth.

The sheets composing the stator are formed by the segments 1 providedwith open notches 2 and teeth 3. These may, for instance be dove-tailedinto the stator frame 4. The rotor segments 5 are provided with notches6 and. teeth 7 and are attached to the massive drum of the rotor bymeans of tenons 8 of progressive curvature and provided in the channels9.

These channels are distributed over the circumference at an arbitrarypitch 2?, and in any desired relation to the polar pitch of the rotorteeth.

The width of the teeth 7 is the same as that of the teeth 3, and thewidth of the notches 2 is double the width of the teeth. In the presentcase, the width of the notches 6 is the same as that of the teeth 7 inaccordance with the general principles previously explained.

As shown in the drawing, the pitch 1) should be preferably chosen insuch a manner that, two consecutive segments 5 are separated by adistance equal to the width of the teeth 7. In this manner, economy willbe made in the sheet iron, because the interval between the segmentsperforms the function of a notch in the rotor. Furthermore, by means ofthis arrangement, each se ent of the sheet iron will be mademechanically independent.

All these arrangements may applied to the case when n=1.

The above described arrangement may also be applied to machines havingfields with albe readily ternating poles of the usual industrial t pe.machines combined. In such a combined ma- Th e purpose of suchapplication is to re uce the number of notches in the armature.

Having described our invention what w claim is: r I

1. A variable impedance high frequency alternator having a rotor and astator whereby a fundamental freqliency is determined for saidalternator by t e speed of the rotor said rotor and stator each havingteeth equal width, and the width of said teeth being equal to times thetooth pitch of the rotor where g is an integer representing the harmonicto be strengthened, the ratio of the number of rotor teeth to statorteeth at least being unity.

2. A variable impedance high fre uency generator comprising a pluralityof a ternators, each alternator having a rotor and stator whereby afundamental frequency is determined for said generator by the speed ofsaid rotors, each of said rotors and stators having teeth, the width ofsaid teeth being times the tooth pitch of said rotors, where g is aninteger greater than unity and representing the harmonic to bestrengthened, said rotors being mechanically coupled and electricallydisplaced by whereby the chosen harmonic will be strengthened and thefundamental will be substantially elimiequal to nated.

3. In a variable impedance high frequency generator, in combination, aslngle stator and g rotors mechanically coupled on one same shaft andelectrically displaced by? said stator and rotors having teeth of equalwidth whereby a fundamental frequency is determined for said generatorby the speed of the rotors, the number of teeth on each rotor beinggreater than the number of stator teeth,

the width of the teeth being equal to times by the number of teeth oneach rotor set being greater than thenumber of stator teeth and thewidth of the teeth being equal to times the tooth pitch of the rotorsets, where g is an integer greater than unity and representing theharmonic to be strengthened, and

means including the q teeth sets for insuring the elimination of thefundamental frequency of all harmonics.

5. A variable impedance high frequency generator having open slots andhavin teeth of equal width on rotor and stator w ereby a fundamental freuency is determined for said generator by t e speed of the rotor, thenumber of rotor teeth being greater than the number of stator teeth andthe width of all the teeth being equal to times the tooth pitch of therotor, where g is an inte er great-- er than unity and representing thearmonic to be strengthened, and the magnetic arts of the rotor beingformed of segments of thin plate provided with teeth and secured inpositlon by means of tenons, the radius of the incurved portions of saidtenons being large with respect to the height of the teeth formmg thepolar projections, and the number of tentolps being independent of thenumber of 6. A variable impedance high frequency alternator having openslots and having teeth of equal width on rotor and stator, whereby afundamental frequency is determined for said alternator by the speed ofthe rotor, the

number of rotor teeth being equal to times the tooth pitch of the rotor,where g is an integer greater than unity and representing the harmonicto be strengthened, the stator being provided with non-magnetic materialinserted at intervals between the active laminations of the stator andthe said material being provided with notches which are partially closedto maintain the windings of the stator on the armature.

7. A high frequency alternator having teeth of equal width on its rotorand stator and the width of the teeth being equal to 1

